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Dependency Injection with Factory Method in Spring

Spring framework provides facility to inject bean using factory method. To do so, we can use two attributes of bean element.

  1. factory-method: represents the factory method that will be invoked to inject the bean.
  2. factory-bean: represents the reference of the bean by which factory method will be invoked. It is used if factory method is non-static.

A method that returns instance of a class is called factory method.

  1. public class A {  
  2. public static A getA(){//factory method  
  3.     return new A();  
  4. }  
  5. }  

Factory Method Types

There can be three types of factory method:

1) A static factory method that returns instance of its own class. It is used in singleton design pattern.

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      1. <bean id="a" class="com.javatpoint.A" factory-method="getA"></bean>  

      2) A static factory method that returns instance of another class. It is used instance is not known and decided at runtime.

      1. <bean id="b" class="com.javatpoint.A" factory-method="getB"></bean>  

      3) A non-static factory method that returns instance of another class. It is used instance is not known and decided at runtime.

      1. <bean id="a" class="com.javatpoint.A"></bean>  
      2. <bean id="b" class="com.javatpoint.A" factory-method="getB" factory-bean="a"></bean>  

      Type 1

      Let's see the simple code to inject the dependency by static factory method.

      1. <bean id="a" class="com.javatpoint.A" factory-method="getA"></bean>  

      Let's see the full example to inject dependency using factory method in spring. To create this example, we have created 3 files.

      1. A.java
      2. applicationContext.xml
      3. Test.java
      A.java

      This class is a singleton class.

      1. package com.javatpoint;  
      2. public class A {  
      3. private static final A obj=new A();  
      4. private A(){System.out.println("private constructor");}  
      5. public static A getA(){  
      6.     System.out.println("factory method ");  
      7.     return obj;  
      8. }  
      9. public void msg(){  
      10.     System.out.println("hello user");  
      11. }  
      12. }  
      applicationContext.xml
      1. <?xml version="1.0" encoding="UTF-8"?>  
      2. <beans  
      3.     xmlns="http://www.springframework.org/schema/beans"  
      4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
      5.     xmlns:p="http://www.springframework.org/schema/p"  
      6.     xsi:schemaLocation="http://www.springframework.org/schema/beans   
      7. http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">  
      8.   
      9. <bean id="a" class="com.javatpoint.A" factory-method="getA"></bean>  
      10.   
      11. </beans>  
      Test.java

      This class gets the bean from the applicationContext.xml file and calls the msg method.

      1. package org.sssit;  
      2. import org.springframework.context.ApplicationContext;  
      3. import org.springframework.context.support.ClassPathXmlApplicationContext;  
      4. public class Test {  
      5. public static void main(String[] args) {  
      6.     ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");  
      7.     A a=(A)context.getBean("a");  
      8.     a.msg();  
      9. }  
      10. }  

      Output:

      private constructor
factory method
hello user

      Type 2

      Let's see the simple code to inject the dependency by static factory method that returns the instance of another class.

      To create this example, we have created 6 files.

      1. Printable.java
      2. A.java
      3. B.java
      4. PrintableFactory.java
      5. applicationContext.xml
      6. Test.java
      Printable.java
      1. package com.javatpoint;  
      2. public interface Printable {  
      3. void print();  
      4. }  
      A.java
      1. package com.javatpoint;  
      2. public class A implements Printable{  
      3.     @Override  
      4.     public void print() {  
      5.         System.out.println("hello a");  
      6.     }  
      7.   
      8. }  
      B.java
      1. package com.javatpoint;  
      2. public class B implements Printable{  
      3.     @Override  
      4.     public void print() {  
      5.         System.out.println("hello b");  
      6.     }  
      7. }  
      PrintableFactory.java
      1. package com.javatpoint;  
      2. public class PrintableFactory {  
      3. public static Printable getPrintable(){  
      4.     //return new B();  
      5.           return new A();//return any one instance, either A or B  
      6. }  
      7. }  
      applicationContext.xml
      1. <?xml version="1.0" encoding="UTF-8"?>  
      2. <beans  
      3.     xmlns="http://www.springframework.org/schema/beans"  
      4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
      5.     xmlns:p="http://www.springframework.org/schema/p"  
      6.     xsi:schemaLocation="http://www.springframework.org/schema/beans   
      7. http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">  
      8.   
      9. <bean id="p" class="com.javatpoint.PrintableFactory" factory-method="getPrintable"></bean>  
      10.   
      11. </beans>  
      Test.java

      This class gets the bean from the applicationContext.xml file and calls the print() method.

      1. package org.sssit;  
      2. import org.springframework.context.ApplicationContext;  
      3. import org.springframework.context.support.ClassPathXmlApplicationContext;  
      4. public class Test {  
      5. public static void main(String[] args) {  
      6.     ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");  
      7.     Printable p=(Printable)context.getBean("p");  
      8.     p.print();  
      9. }  
      10. }  

      Output:

      hello a

      Type 3

      Let's see the example to inject the dependency by non-static factory method that returns the instance of another class.

      To create this example, we have created 6 files.

      1. Printable.java
      2. A.java
      3. B.java
      4. PrintableFactory.java
      5. applicationContext.xml
      6. Test.java

      All files are same as previous, you need to change only 2 files: PrintableFactory and applicationContext.xml.

      PrintableFactory.java
      1. package com.javatpoint;  
      2. public class PrintableFactory {  
      3. //non-static factory method  
      4. public Printable getPrintable(){  
      5.     return new A();//return any one instance, either A or B  
      6. }  
      7. }  
      applicationContext.xml
      1. <?xml version="1.0" encoding="UTF-8"?>  
      2. <beans  
      3.     xmlns="http://www.springframework.org/schema/beans"  
      4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
      5.     xmlns:p="http://www.springframework.org/schema/p"  
      6.     xsi:schemaLocation="http://www.springframework.org/schema/beans   
      7. http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">  
      8.   
      9. <bean id="pfactory" class="com.javatpoint.PrintableFactory"></bean>  
      10. <bean id="p" class="com.javatpoint.PrintableFactory" factory-method="getPrintable"   
      11. factory-bean="pfactory"></bean>  
      12.   
      13. </beans>  

      Output:

      hello a
      Next TopicSpring AOP Tutorial




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